Lonely high school student Kei Kurono isolates himself out of a growing cynicism toward his fellow man and the cruelty they are capable of enacting. One day, while waiting to take the subway to school, Kei's classmate Masaru Katou leaps onto the tracks in an effort to save a drunk man. Driven by an uncharacteristic desire to rescue someone else, Kei follows Katou down into danger. While successful in saving him, the two boys are killed by the train.
Kei wakes up beside Katou in an apartment full of strangers and furnished by a giant black orb with a glass-like outer surface. After finding out that everyone in the room has recently died, words appear on the black ball tasking them with killing a strange creature. The ball equips Kei and the others with power suits and mysterious guns before sending them off to collect this bizarre bounty.